Digital Sound Corporation

Nam H Pham

James M Underwood

Reliable access to audio and facsimile message storage and retrieval systems is accomplished by employing a listening procedure to differentiate voice message clients from fax clients and, upon identifying a fax client, performing an extended listening procedure to differentiate between a sending fax client and a retrieving fax client. During the listening procedure, the system generates a ring tone, immediately after connecting the call, comparable in duration to that normally expected by a caller during a typical call attempt, thereby rendering the listening procedure transparent to a human caller. The masked listening procedure allows detection of standard calling fax machine, polling fax machines and accommodates a blind polling procedure for use with fax machines not equipped for standard call in polling. Blind polling is accomplished by monitoring a fax receiver in the system for a called station tone (CED) or if a CED tone is missed by the system, detection of V.21/V.27 transmissions allows the establishing of a messaging session. Absence of CED tone, CNG tone or V.21 or V.27 transmissions during the listening period causes the system to classify the call as a voice call and produce voice prompts to a presumed human caller. Continuous monitoring for CNG tone detection allows reclassification of the call as a fax sending call, allowing combination voice and fax messages to be recorded.

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Carpinteria, CA, United States of America

Nam H Pham